CN111852431B - Optimization method and device for slotted net structure parameters in slotted net fracturing - Google Patents

Optimization method and device for slotted net structure parameters in slotted net fracturing Download PDF

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CN111852431B
CN111852431B CN202010835097.3A CN202010835097A CN111852431B CN 111852431 B CN111852431 B CN 111852431B CN 202010835097 A CN202010835097 A CN 202010835097A CN 111852431 B CN111852431 B CN 111852431B
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permeability
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CN111852431A (en
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曾凡辉
张涛
杨铠嵽
郭建春
任文希
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Southwest Petroleum University
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    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/25—Methods for stimulating production
    • E21B43/26—Methods for stimulating production by forming crevices or fractures
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B43/00—Methods or apparatus for obtaining oil, gas, water, soluble or meltable materials or a slurry of minerals from wells
    • E21B43/25—Methods for stimulating production
    • E21B43/26—Methods for stimulating production by forming crevices or fractures
    • E21B43/267—Methods for stimulating production by forming crevices or fractures reinforcing fractures by propping
    • E—FIXED CONSTRUCTIONS
    • E21—EARTH DRILLING; MINING
    • E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
    • E21B49/00—Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/20—Design optimisation, verification or simulation

Abstract

The invention provides a method and a device for optimizing structural parameters of a slotted net in slotted net fracturing, wherein the method comprises the following steps: based on a tree fractal theory, establishing a tree bifurcation network structure parameter relation, and determining the total volume of tree bifurcation network cracks; based on a tree fractal theory, establishing a mass flow relation of a complex gap network region in consideration of gap width change, and determining a permeability model of a tree-shaped branched network crack through a mass flow relation; and calculating the permeability under different structural parameter combinations under the condition of determining the total volume of the tree-shaped branched network cracks, and determining the optimal structural parameters of the tree-shaped branched network cracks according to the calculation result of the permeability. The method and the device for optimizing the fracture network structure parameters in fracture network fracturing provided by the invention overcome the technical problem that the structure parameters in a tree-shaped branched network structure cannot be optimized in the prior art, and the tree-shaped fractal theory is adopted to describe the fracture form, so that the fracture form is more consistent with the fracture form.

Description

Optimization method and device for slotted net structure parameters in slotted net fracturing
The technical field is as follows:
the invention relates to the field of petroleum and natural gas development, in particular to a method and a device for optimizing structural parameters of a fracture network in fracture network fracturing.
Background
The shale gas reservoir has low permeability and poor flow capacity, and hydraulic fracturing is an important means for developing the shale gas reservoir, wherein fracture network fracturing is the most efficient way for developing shale gas. After the shale reservoir is fractured by the seam network, a complex seam network is formed in the matrix, so that the seepage characteristic of the matrix is changed, and the yield of shale gas is improved. The structural morphology of the slotted net is a key factor influencing the permeability of the reconstruction zone and the dosage of the proppant.
In the prior art, according to the expansion characteristics of the seam net, a complex seam net structure can be regarded as a tree-shaped branched network structure. The reasonable seam network structure design is an important guarantee for improving the flowing capacity and permeability of the shale gas in the seam network, and is also a key factor for effectively optimizing the seam network fracturing propping agent and efficiently and economically developing shale gas resources. However, no method is available at present for optimizing the structure parameters (such as length ratio, width ratio, etc.) in the tree-like branched network structure.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, provides a method and a device for optimizing structural parameters of a slotted network in slotted network fracturing, solves the technical problem that the structural parameters in a tree-shaped branched network structure cannot be optimized in the prior art, can optimize the structural parameters of the slotted network suitable for reservoir conditions, and provides theoretical guidance for fracturing construction.
The purpose of the invention is realized by the following technical scheme.
In a first aspect, the present application provides a method for optimizing structural parameters of a slotted net in slotted net fracturing, comprising the steps of:
(1) based on a tree fractal theory, establishing a tree bifurcation network structure parameter relation, and determining the total volume of tree bifurcation network cracks;
(2) based on a tree fractal theory, establishing a mass flow relation of a complex gap network region in consideration of gap width change, and determining a permeability model of a tree-shaped branched network crack through a mass flow relation;
(3) and calculating the permeability under different structural parameter combinations under the condition of determining the total volume of the tree-shaped branched network cracks, and determining the optimal structural parameters of the tree-shaped branched network cracks according to the calculation result of the permeability.
Further, the tree-like bifurcation network fracture total volume expression in the step (1) is as follows:
Figure BDA0002639368810000011
in the formula, V is the total volume of the tree-shaped branched network cracks; subscript k is the serial number of the tree network stage; m is the tree network level; a is the k-th crack height; bkThe k-th crack width; lkThe length of the k-th crack is the length of the crack; n is the tree network bifurcation number; r is the microcrack aspect ratio; b0The initial crack width; l0The initial crack length; alpha is the seam width ratio; gamma is the slot lengthAnd (4) the ratio.
Further, in the step (2), the mass flow relationship includes one or more modes of migration of viscous flow, surface diffusion and knudsen diffusion of shale gas.
Further, in the step (2), when the permeability model of the tree-shaped branched network fracture is determined through the mass flow relational expression, the permeability model of the tree-shaped branched network fracture is established based on the generalized darcy law.
Further, in the step (3), the permeability under different structural parameter combinations is calculated under the condition of determining the total volume of the tree-shaped branched network cracks, when the optimal structural parameters of the tree-shaped branched network cracks are determined according to the calculation result of the permeability,
determining the total volume of the tree-shaped branched network fracture through the volume of the proppant, and calculating the permeability of the combination of different width ratios and length ratios under the condition of the known modification length of the tree-shaped branched network fracture;
and obtaining the optimal structural parameter combination by comparing the permeability results.
Further, the method also comprises the step of carrying out fracturing pump injection programming by using the result of the optimal structural parameter.
In a second aspect, the present application provides an apparatus for optimizing structural parameters of a slotted-net in slotted-net fracturing, wherein the apparatus comprises:
the tree-shaped bifurcation network crack total volume determining module is used for establishing a tree-shaped bifurcation network structure parameter relation by utilizing a tree-shaped fractal theory and determining the tree-shaped bifurcation network crack total volume;
the permeability determining module of the tree-shaped branched network cracks is used for establishing a mass flow relation of a complex slit network region considering slit width change by utilizing a tree-shaped fractal theory and determining a permeability model of the tree-shaped branched network cracks through a mass flow relation;
and the optimal structure parameter determining module is used for calculating the permeability under different structure parameter combinations under the condition of determining the total volume of the tree-shaped branched network cracks and determining the optimal structure parameters of the tree-shaped branched network cracks according to the calculation result of the permeability.
Further, the tree-like bifurcation network fracture total volume expression is as follows:
Figure BDA0002639368810000021
in the formula, V is the total volume of the tree-shaped branched network cracks; subscript k is the serial number of the tree network stage; m is the tree network level; a is the k-th crack height; bkThe k-th crack width; lkThe length of the k-th crack is the length of the crack; n is the tree network bifurcation number; r is the microcrack aspect ratio; b0The initial crack width; l0The initial crack length; alpha is the seam width ratio; gamma is the slot length ratio.
Further, the mass flow relationship includes one or more modes of migration of shale gas viscous flow, surface diffusion, knudsen diffusion.
Further, the optimal configuration parameter determination module further includes:
the permeability calculation unit is used for determining the total volume of the tree-shaped branched network fracture through the volume of the propping agent, and calculating the permeability of different width ratios and length ratio combinations under the condition of the known transformation length of the tree-shaped branched network fracture;
and the permeability comparison unit is used for comparing permeability results to obtain an optimal structural parameter combination.
Compared with the prior art, the invention has the beneficial technical effects that:
(1) the invention solves the technical problem that the structure parameters in the tree-shaped branched network structure can not be optimized in the prior art.
(2) The method is based on the idea of determining the volume of the propping agent, and can calculate the seam-net permeability under different structural parameter combinations.
(3) According to the method, multiple migration forms of the shale gas, such as one or more of slip flow, Knudsen diffusion and surface diffusion, can be considered according to the actual occurrence and seepage conditions of the reservoir shale.
(4) The invention can establish the structural parameter description relation of the tree-shaped branched network by adopting the tree-shaped fractal theory, and the structure parameter description relation is more consistent with the actual form of the tree-shaped branched network.
Drawings
Fig. 1 is a schematic structural diagram of a slotted-net fractured tree-like bifurcated network.
FIG. 2 is a graph of the change in gap web permeability versus width ratio.
FIG. 3 is a graph of seam web permeability versus length ratio.
FIG. 4 shows the seam web permeability for different combinations of width ratio α and length ratio γ.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
(1) Based on a tree fractal theory, establishing a tree bifurcation network structure parameter relation, and determining the total volume of tree bifurcation network cracks;
as shown in the attached fig. 1 of the specification, the complex slotted net structure formed after slotted net fracturing can be regarded as a tree-shaped branched network, so that the complex slotted net structure is obtained through a tree-shaped fractal theory:
Figure BDA0002639368810000031
Figure BDA0002639368810000032
Figure BDA0002639368810000033
in the formula bkThe k-th crack width is m; b0M is the initial crack width; lkThe length of the k-th crack is m; l0M is the initial crack length; leIs a number of tree network horizontal lengths (transformation lengths), m; alpha is the seam width ratio and is dimensionless; gamma is the length ratio of the seam and is dimensionless; theta is the arborescent bifurcation angle, °; m is a tree network level and is dimensionless;
and superposing the volumes of all the cracks to obtain the total volume of the tree-shaped branched network cracks, wherein the expression of the total volume of the tree-shaped branched network cracks is as follows:
Figure BDA0002639368810000041
in the formula, n is a tree network branching number and is dimensionless; r is the microcrack aspect ratio, dimensionless;
(2) based on a tree fractal theory, establishing a mass flow relation of a complex gap network region in consideration of gap width change, and determining a permeability model of a tree-shaped branched network crack through a mass flow relation;
taking the gas flow of the kth-stage fracture as an example, the mass flow relationship is derived, and the detailed process is as follows:
the shale pore characteristics determine the existence of multiple mobile migration modes of gas in micropores, such as viscous flow, surface diffusion, Knudsen diffusion and the like, and a person skilled in the art can establish a corresponding shale gas mass flow relation according to different occurrence and migration characteristics of an actual shale reservoir, and establish a corresponding mass flow relation when the viscous flow, the surface diffusion and the Knudsen diffusion exist in the shale pores at the same time.
Considering the influence of the slippage effect and the crack shape on the mass flow, the mass flow of the tree fractal kth crack gas viscous flow is as follows:
Figure BDA0002639368810000042
in the formula, the subscript k is the crack grade number, phi is the microcrack porosity, and the dimension is zero; tau is microcrack tortuosity and has no dimension; a (r) is a microcrack cross-section shape factor which influences continuous flow, and has no dimension; r is the aspect ratio, dimensionless; b is the seam width, m; a is the seam height, m; μ is the gas viscosity, mPas; p is the formation pressure, Mpa; m is gas molar mass, kg/mol; r is a gas constant having a value of 8.314 J.mol-1K-1(ii) a T is the formation temperature, K; beta is a rare effect coefficient and is dimensionless; t is the gas slip systemNumber, dimensionless; j. the design is a squarevMass flow, kg.s, for the sliding flow of microcracked gases-1。
Taking the knudsen number as a constant, the total mass flow of the dendriform fractal crack gas slipping flow is as follows:
Jv＝nkJvk (6)
the k-th pressure drop of the tree-shaped fractal crack gas slippage flow is as follows:
Figure BDA0002639368810000043
the total pressure drop for the tree-shaped fractal fracture gas slip flow is:
Figure BDA0002639368810000051
the total mass flow rate of substituting equation (3) into equation (8) tree-shaped fractal fracture gas continuous flow can be expressed as:
Figure BDA0002639368810000052
the mass flow of the k-th-order crack gas Knudsen diffusion of the tree fractal is as follows:
Figure BDA0002639368810000053
in the formula JkMass flow rate of gas Knudsen diffusion, kg.s-1(ii) a B (r) is a microcrack form factor, dimensionless, that affects knudsen diffusion.
The total mass flow of the denudsen diffusion of the tree-shaped fractal crack gas is as follows:
Jk＝nkJkk (11)
the k-th order pressure drop of the denudsen diffusion of the tree-shaped fractal crack gas is as follows:
Figure BDA0002639368810000054
the total pressure drop of the tree-shaped fractal microcrack gas knudsen diffusion is as follows:
Figure BDA0002639368810000055
the total mass flow of substituting equation (3) into the tree-shaped fractal fracture gas knudsen diffusion of equation (13) can be expressed as:
Figure BDA0002639368810000056
the mass flow rate of the surface diffusion of the k-th-level crack gas with the tree fractal structure is as follows:
Figure BDA0002639368810000061
the total mass flow of the denudsen diffusion of the tree-shaped fractal crack gas is as follows:
Jsurface＝nkJsurfacek (16)
the k-th order pressure drop of the denudsen diffusion of the tree-shaped fractal crack gas is as follows:
Figure BDA0002639368810000062
the total pressure drop of the tree-shaped fractal microcrack gas knudsen diffusion is as follows:
Figure BDA0002639368810000063
the total mass flow of substituting equation (3) into the equation (18) tree-shaped fractal fracture gas knudsen diffusion can be expressed as:
Figure BDA0002639368810000064
flux expression of Darcy's formula:
Figure BDA0002639368810000065
consider slot width dynamics:
b＝b0+Δbt (21)
wherein:
Figure BDA0002639368810000066
in the formula pobIs overburden rock pressure, MPa; p is a radical ofpPore pressure, MPa. p is a radical ofob0Initial overburden rock pressure, MPa; p is a radical ofp0Initial pore pressure, Mpa; c. CfIs the fracture compression factor, MPa-1(ii) a E is the Young modulus of rock, MPa; upsilon is the Poisson ratio of rock and has no dimension; sLIs Langmuir strain, m; p is a radical ofLLangmuir pressure, MPa.
The formula (21) and the formula (22) are respectively substituted for the formula (9), (14) and the formula (19), and meanwhile, the joint type (20) can respectively obtain permeability equations of slip flow, Knudsen diffusion and surface diffusion.
Figure BDA0002639368810000071
Figure BDA0002639368810000072
Figure BDA0002639368810000073
The total permeability of the tree-shaped seam network considering the dynamic change of the seam width is as follows:
Kt＝Kv+Kk+Ksurface (26)
namely, the permeability expression obtained by calculation in the relational expression is a permeability model of the tree-shaped branched network fracture.
(3) And calculating the permeability under different structural parameter combinations under the condition of the total volume of the tree-shaped branched network cracks, and determining the optimal structural parameter according to the calculation result of the permeability.
When the proppant is continuously laid and uniformly filled in the network of cracks, the volume of the proppant is in direct proportion to the total volume of the cracks in the tree-shaped branched network. By determining the total volume of the tree-like branched network fracture (i.e. the volume of the proppant used is constant), a set of basic parameters is first given to calculate the volume of a tree-like branched network (in the example of the present invention, 2.4 × 10-3m3) As reference volume, the length l is reconstructed by knowingeCalculating the level m of the tree-shaped fractal slotted net, calculating the ratio combination of different width ratios alpha and length ratios gamma under the fixed volume by combining the volume of the standard tree-shaped slotted net, finally bringing the ratio combination into a permeability model, and comparing permeability results to obtain the optimal structural parameter combination.
Example calculation
In order to make the technical steps and principles of the present invention more understandable to those skilled in the art, the following examples are used to explain in detail, and the basic parameters of the simulation used in the examples are shown in table 1.
TABLE 1 simulation basic data Table
Figure BDA0002639368810000074
Figure BDA0002639368810000081
(2) Analysis of calculation results
As can be seen from the calculation results of FIG. 2, the permeability of the slot network has a trend of decreasing first and then increasing with the increase of the formation pressure, wherein the permeability is the lowest when the formation pressure is 6 MPa. The dynamic change of the seam width is considered, so that the seam width changes along with the change of the formation pressure; the permeability increases with decreasing width ratio α, and this effect is more pronounced at high pressures (30MPa), indicating that width ratio α is inversely related to the seam network permeability at higher formation pressures.
As can be seen from the calculation results of fig. 3, as the length ratio γ increases, the permeability also increases, and this effect hardly changes with a decrease in the formation pressure, and the length ratio γ is positively correlated with the permeability, but the sensitivity is lower than the width ratio α.
As can be seen from the calculation results in fig. 4, the permeability can be calculated by matching and combining the width ratio α and the length ratio γ obtained by determining the volume of the tree-like slit network. The larger the calculation result, the better the flow ability of the slotted net, and the proppant meets the assumption of continuous filling and uniform laying, so the proppant dosage is equivalent to the volume of the tree-shaped slotted net. FIG. 4 shows the volume of the network at the tree seam of 2.4X 10-3m3The ratio of width α to length γ is 0.58 and the ratio of length γ is 0.75. During fracture network fracturing construction, under the condition of the same proppant dosage, the width ratio alpha of the fracture network is reduced, the length ratio gamma of the fracture network is increased to obtain higher fracture network permeability, the flowing capacity of fluid in the fracture network is enhanced, and the fracture network fracturing effect is improved.
Thus, in the reconstruction of the length le0.4m, first level slit width b0When the width ratio alpha is 1mm and the optimal width ratio alpha is 0.58, the width of each stage of the crack of the tree-shaped crack network and the mesh number of the propping agent can be calculated by the method in the invention in an optimized way as shown in the table 2, so that the technical personnel in the field can utilize the optimized result to carry out the program design of the fracturing pump injection.
TABLE 2 Tree-shaped seam width and proppant mesh number calculation table
Figure BDA0002639368810000091
While the present invention has been described in detail by way of the embodiments, it should be understood that the present invention is not limited to the embodiments disclosed herein, but is intended to cover other embodiments as well. But all the modifications and simple changes made by those skilled in the art without departing from the technical idea and scope of the present invention belong to the protection scope of the technical solution of the present invention.

Claims (6)

1. A method for optimizing structural parameters of a slotted net in slotted net fracturing is characterized by comprising the following steps:
(1) based on a tree fractal theory, establishing a tree bifurcation network structure parameter relation, and determining the total volume of tree bifurcation network cracks;
the tree-shaped branched network crack total volume expression is as follows:
Figure FDA0003512900760000011
in the formula, V is the total volume of the tree-shaped branched network cracks; subscript k is the serial number of the tree network stage; m is the tree network level; a is the k-th crack height; bkThe k-th crack width; lkThe length of the k-th crack is the length of the crack; n is the tree network bifurcation number; r is the microcrack aspect ratio; b0The initial crack width; l0The initial crack length; alpha is the seam width ratio; gamma is the slot length ratio;
(2) based on a tree fractal theory, establishing a mass flow relation of a complex gap network region in consideration of gap width change, and determining a permeability model of a tree-shaped branched network crack through a mass flow relation;
the permeability model of the tree-like bifurcation network fracture is as follows:
Kt＝Kv+Kk+Ksurface
Figure FDA0003512900760000012
Figure FDA0003512900760000013
Figure FDA0003512900760000014
wherein Kt isPermeability of tree-like branched network fractures(ii) a Kv is the slip flow permeability; kk is the permeability of knudsen diffusion; ksource is the permeability of surface diffusion; a (r) is the microcrack cross-sectional shape factor that affects continuous flow; r is the aspect ratio; phi is the microcrack porosity; μ is the gas viscosity; l0The initial crack length; b0The initial crack width;
Figure FDA0003512900760000021
tau is microcrack tortuosity; beta is a rare effect coefficient; knb is the Knudsen coefficient; t is the gas slippage coefficient; gamma is the slot length ratio; theta is a tree bifurcation angle; m is the tree network level; beta is a rare effect coefficient; m is the tree network level;
b (r) is a microcrack form factor that affects Knudsen diffusion; ρ is the gas molecular density; m is the gas molar mass; r is a gas constant; t is the formation temperature; dsIs the surface diffusion coefficient; csmaxThe maximum concentration of the surface adsorbed gas; p is a radical ofLLangmuir pressure; p is the formation pressure;
(3) calculating permeability under different structural parameter combinations under the condition of determining the total volume of the tree-shaped branched network cracks, and determining the optimal structural parameters of the tree-shaped branched network cracks according to the calculation result of the permeability;
in the step (3), the permeability under different structural parameter combinations is calculated under the condition of determining the total volume of the tree-shaped branched network fracture, and when the optimal structural parameter of the tree-shaped branched network fracture is determined according to the calculation result of the permeability, the method further includes:
determining the total volume of the tree-shaped branched network fracture through the volume of the proppant, and calculating the permeability of the combination of different width ratios and length ratios under the condition of the known modification length of the tree-shaped branched network fracture;
and obtaining the optimal structural parameter combination by comparing the permeability results.
2. The method for optimizing structural parameters of a trawl door in a trawl door fracture as claimed in claim 1, wherein in step (2), the mass flow relationship comprises one or more modes of migration of shale gas viscous flow, surface diffusion and knudsen diffusion.
3. The method for optimizing fracture network structure parameters in fracture network fracturing as claimed in claim 1, wherein in the step (2), when determining the permeability model of the tree-shaped branched network fracture through the mass flow relational expression, the permeability model of the tree-shaped branched network fracture is established based on darcy's law.
4. The method for optimizing fracture network structural parameters in a fracture network fracture of claim 1, further comprising using the results of the optimal structural parameters for fracture pump programming.
5. An apparatus for optimizing structural parameters of a slotted-net in slotted-net fracturing, the apparatus comprising:
the tree-shaped bifurcation network crack total volume determining module is used for establishing a tree-shaped bifurcation network structure parameter relation by utilizing a tree-shaped fractal theory and determining the tree-shaped bifurcation network crack total volume;
the tree-shaped branched network crack total volume expression is as follows:
Figure FDA0003512900760000022
in the formula, V is the total volume of the tree-shaped branched network cracks; subscript k is the serial number of the tree network stage; m is the tree network level; a is the k-th crack height; bkThe k-th crack width; lkThe length of the k-th crack is the length of the crack; n is the tree network bifurcation number; r is the microcrack aspect ratio; b0Is an initialThe width of the crack is wide; l0The initial crack length; alpha is the seam width ratio; gamma is the slot length ratio;
the permeability determining module of the tree-shaped branched network cracks is used for establishing a mass flow relation of a complex slit network region considering slit width change by utilizing a tree-shaped fractal theory and determining a permeability model of the tree-shaped branched network cracks through a mass flow relation;
the permeability model of the tree-like bifurcation network fracture is as follows:
Kt＝Kv+Kk+Ksurface
Figure FDA0003512900760000031
Figure FDA0003512900760000032
Figure FDA0003512900760000033
wherein Kt isPermeability of tree-like branched network fractures(ii) a Kv is the slip flow permeability; kk is the permeability of knudsen diffusion; ksource is the permeability of surface diffusion; a (r) is the microcrack cross-sectional shape factor that affects continuous flow; r is the aspect ratio; phi is the microcrack porosity; μ is the gas viscosity; l0The initial crack length; b0The initial crack width;
Figure FDA0003512900760000034
tau is microcrack tortuosity; beta is a rare effect coefficient; knb is the Knudsen coefficient; t is the gas slippage coefficient; gamma is the slot length ratio; theta is a tree bifurcation angle; m is the tree network level; beta is a rare effect coefficient; m is the tree network level;
b (r) is a microcrack shape factor affecting Knudsen diffusionA seed; ρ is the gas molecular density; m is the gas molar mass; r is a gas constant; t is the formation temperature; dsIs the surface diffusion coefficient; csmaxThe maximum concentration of the surface adsorbed gas; p is a radical ofLLangmuir pressure; p is the formation pressure;
the optimal structure parameter determining module is used for calculating the permeability under different structure parameter combinations under the condition of determining the total volume of the tree-shaped branched network cracks and determining the optimal structure parameters of the tree-shaped branched network cracks according to the calculation result of the permeability;
the method specifically comprises the following steps: determining the total volume of the tree-shaped branched network fracture through the volume of the proppant, and calculating the permeability of the combination of different width ratios and length ratios under the condition of the known modification length of the tree-shaped branched network fracture;
and obtaining the optimal structural parameter combination by comparing the permeability results.
6. The apparatus for optimizing slotted network structural parameters in slotted network fracturing as claimed in claim 5, wherein said mass flow relationships comprise one or more modes of migration of shale gas viscous flow, surface diffusion, knudsen diffusion.
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